1. FIELD OF INVENTION
This invention relates to integrated circuits and more particularly to integrated circuits for interconnecting a communication line to any one of a plurality of communication lines.
2. DISCUSSION OF THE PRIOR ART
In numerous communication systems, such as a telephone switching network, a transmission path is provided between a given pair of input lines and any number of output lines by selectively establishing cross point connections in a switching matrix.
It has been suggested to use latching type semiconductors, such as silicon controlled rectifiers or silicon controlled switches, as cross point devices to provide connections between input and output transmission lines or communication lines. Basically, a latching semiconductor is set to a low impedance or conducting state by the application of signals to its gate electrode. Once this device conducts the gate electrode control signal is no longer required and the device latches into a set or conductive state. Thus, once the semiconductor latch is set no additional signal is required to maintain the latched position.
Furthermore, a latching type of device is desirable in that it possesses in high impedance, low current characteristic when residing in a nonconducting state, and a low impedance high current characteristic when in a conducting state. The device, therefore, provides excellent isolation between its gate electrode and its input and output electrodes in order to avoid erroneous switching due to system transients. Moreover, these devices possess excellent transient characteristics for communication purposes and are capable of high frequency operation.
In one known prior art system, latching semiconductor devices are employed as cross point switches for directly interconnecting coordinately disposed communication lines. Essentially, logic circuitry connected to addressing means is employed to select and set the latching semiconductor device in order to interconnect a particular cross point. The connection is maintained by having the switch conduct a current greater than its holding current. However, this type of arrangement suffers from two major problems. Firstly, even though the selection operation of a particular latchable semiconductor device is relatively straight forward from a circuit and complexity standpoint, the disconnect implementation requires the actual switching of current sources internal to the communication system in order to reduce the current in the latchable semiconductor device below the required holding current. Naturally, this increased circuitry becomes magnified manyfold when employed in the environment of a cross point switching matrix. Secondly, the selection and disconnect is performed internal to the communication system and thus signal conditions on the communication lines have the potential of interrupting the cross point condition as the latching element is located directly in the transmission path.